High solids coating composition adapted for use as automotive topcoat-#5

Abstract

A fast curing, high solids coating composition that is adapted for use as an automotive topcoat and which upon curing forms a hard, glossy, durable coating exhibiting excellent resistance to solvents and water. The coating composition contains greater than about 60 percent by weight of nonvolatile solids and, exclusive of pigments, solvents and other nonreactive components, consists essentially of: (A) a polyepoxide resin having a number average molecular weight (M n ) of between about 140 and about 3,000; (B) a reactive catalyst comprising at least one hydroxy functional organophosphate ester selected from certain mono- and diesters of phosphoric acid; (C) an amino resin crosslinking agent; and (D) optionally, a hydroxy functional additive. The hydroxy functional organophosphate ester is included in the composition in an amount sufficient to provide between about 0.67 and about 1.4 equivalents of acid functionality for each equivalent of epoxy functionality in the polyepoxide resin and the amine-aldehyde crosslinking agent is included in the composition in an amount sufficient to provide at least about 0.4 equivalents of nitrogen crosslinking functionality for each equivalent of hydroxy functionality included in the composition.

What is claimed is: 
     
       1. A thermosetting coating composition adapted for low temperature bake applications which contains greater than about 60% by weight of nonvolatile solids, and which, exclusive of pigments, solvents and other nonreactive components, consists essentially of: (A) a polyepoxide resin having a number average molecular weight (M n ) of between about 140 and about 3,000;   (B) a reactive catalyst comprising at least one organophosphate ester having the formula: ##STR3##  wherein n=1 to 2 and R is selected from the group consisting of mono or dihydroxy alkyl, cycloalkyl, or aryl radicals;   (C) an amine-aldehyde crosslinking agent; and   (D) up to about 45 weight percent based on the total weight of (A), (B), (C) and (D) of a hydroxy functional additive having a number average molecular weight (M n ) of between about and about 6000, said organophosphate ester being included in said composition in an amount sufficient to provide between about 0.67 and about 1.4 equivalents of acid functionality for each equivalent of epoxy functionality on said polyepoxide resin, and said amine-aldehyde crosslinking agent being included in said composition in an amount sufficient to provide at least about 0.4 equivalents of nitrogen crosslinking functionality for each equivalent of hydroxy functionality included in said composition either as (i) an organic hydroxyl group on said organophosphate ester, (ii) a hydroxyl group on said hydroxy functional additive, or (iii) as a result of esterification of said epoxy functionality of said polyepoxide resin during cure of said coating composition.   
     
     
       2. A composition in accordance with claim 1 wherein said polyepoxide resin is selected from the group consisting of aliphatic, cycloaliphatic and aromatic polyepoxides having a number average molecular weight of between about 300 and about 2,000. 
     
     
       3. A composition in accordance with claim 1 wherein said hydroxy functional organophosphate ester is an ester wherein R is a mono or dihydroxy alkyl, cycloalkyl or aryl radical containing 3 to 10 carbon atoms. 
     
     
       4. A composition in accordance with claim 1 wherein said organophosphate ester is a monoester. 
     
     
       5. A composition in accordance with claim 1 wherein said organophosphate ester is a diester. 
     
     
       6. A composition in accordance with claim 1, wherein said organophosphate ester is a mixture of mono- and diesters. 
     
     
       7. A composition in accordance with claim 6 wherein said hydroxy functional organophosphate ester is an ester wherein R is a mono- or dihydroxy alkyl, cycloalkyl or aryl radical containing 3 to 10 carbon atoms. 
     
     
       8. A composition in accordance with claim 6 wherein at least a portion of said organophosphate esters are esters wherein R is mono- or dihydroxy alkyl radical containing 3 to 10 carbon atoms. 
     
     
       9. A composition in accordance with claim 1 wherein said reactive catalyst including said organophosphate ester is the reaction product of an excess of an alkyl, cycloalkyl or aryl diol or triol and phosphorus pentoxide. 
     
     
       10. A composition in accordance with claim 1 wherein said reactive catalyst including said hydroxy functional organophosphate ester is the reaction produce of an excess of an alkyl, cycloalkyl or aryl triol in which at least one of the hydroxyl groups is secondary and phosphorus pentoxide. 
     
     
       11. A composition in accordance with claim 1 wherein said reactive catalyst including said hydroxy functional organophosphate ester is the reaction product of an alkyl, cycloalkyl or aryl monoepoxide and phosphoric acid in a molar ratio of between about 1:1 and about 2:1. 
     
     
       12. A composition in accordance with claim 11 wherein said monoepoxide also bears hydroxyl functionality. 
     
     
       13. A composition in accordance with claim 11 wherein said monoepoxide is selected from monoepoxy esters, monoepoxy ethers and alkylene oxides. 
     
     
       14. A composition in accordance with claim 1 wherein said amine-aldehyde crosslinking agent is selected from the group consisting of condensation products of formaldehyde with melamine, substituted melamine, urea, benzoguanamine, and substituted benzoquanamine, and mixtures of said condensation products, and is included in an amount sufficient to provide between about 0.6 and about 2.1 equivalents of nitrogen crosslinking of functionality per equivalent of hydroxy functionality. 
     
     
       15. A composition in accordance with claim 1 wherein said hydroxy functional additive is selected from the group consisting of (i) hydroxy functional polyesters, (ii) hydroxy functional polyethers, (iii) hydroxy functional oligoesters, (iv) monomeric polyols, (v) hydroxy functional copolymers formed from monoethylenically unsaturated monomers, one or more of which bears hydroxy functionality and which is included in said copolymer in amounts ranging from about 10 to about 30 weight percent of said copolymer, and (vi) mixtures of (i)-(v). 
     
     
       16. A composition in accordance with claim 1 wherein said organophosphate ester is included in said composition in an amount sufficient to provide between about 1 and about 1.2 equivalents of acid functionality for each equivalent of epoxy functionality on said polyepoxide resin.